This invention relates in general to eye wear, and in particular, to a method and apparatus for shaping wire frames for holding lenses.
Many eyeglass frames are made of metal. The metal forms the temples that loop over a person's ears, metal is used to form the bridge between two lenses, and the lenses are held in bent metal frames called eyewires. Each wire has its main curvature termed the shape curve about the optical axis of the lens which will fit into it. In order to conform to the edge of the lens, whose surface is spherical, it has a secondary curvature, termed the base curve.
In order to form eyewires, a wire is fed from a spool, straightened, and then bent at sequential bending stations to impart the first or base curve and the second or shape curve to the eyewire. In prior art systems, curves are imparted to the wires using a series of rollers with movable elements at the end of the bender. The movable elements at the end of the bender are displaceable against the wire. The greater the displacement of the bending roller against the wire, the more curvature is imparted to the wire as it passes over the roller. However, it is only possible to bend the wire in one axis at one station. That is, there is no currently available technique for simultaneously imparting both the base curve and the shape curve to the wire.
As such, one of the problems associated with prior art techniques has been the coordination of the first and second bending stations in order to impart the shape curve to the wire that has been impressed with a base curve. In order to solve this problem, the prior art techniques have relied upon bending stations having relatively small rollers and by positioning the bending stations as close as possible to one another. As such, with closely positioned bending stations and small rollers (perhaps as small as one-quarter inch) the wire is bent as though the base and shape curves are simultaneously made at one point on the wire. In other words, the distance that the wire travels between the first and the second bending station is effectively ignored.
Even with small bending rollers, there is nevertheless a finite differential in wire travel between the first and second bending stations. This finite distance contributes to errors in bending such that many eyewires are rejected in manufacture. Such prior art systems have not included on-line correction of bending to accommodate variations in wire. It is well known that there are significant metallurgical differences between the wire at one end of a spool and the wire at the other end. Thus, as wire is withdrawn from a spool and formed into eyewires, the wire material itself will vary from segment to segment as it passes through the two bending stations. However, in such prior art bending systems, there is no provision for monitoring and on-line altering the bending characteristics of the two bending stations in order to accommodate changes in the wire.
Such prior art eyewinder systems, due to the close proximity of the first and second bending stations, introduce large, and undesirable stresses in the eyewires. The latter is due to the sharp radii of curvature of the small bending rollers as well as the near simultaneous bending in orthoganol directions imparted by the two stations. As such, the wires become unduly stressed and many fail to conform to acceptable manufacturing specifications.
Still another disadvantage of prior art systems is that finished eyewires are only inspected by a manual optical comparison of the eyewire to metal fixtures of the desired shape. Because such techniques are time consuming, cumbersome and inaccurate, inspections are infrequent and thereby result in poor quality control.